This invention relates to semiconductor III-V alloy compounds, as well as to a method of making III-V alloy compounds for use in diode lasers.
The importance of semiconductor emitters and detectors is rapidly increasing along with progress in the opto-electronic field, such as optical fiber communication, optical data processing, storage and solid state laser pumping.
GaN-based compounds are the most promising material system for high performance and economical ultraviolet (UV) emitters photodetectors. With a bandgap energy from 3.4 eV to 6.2 eV, UV photodetectors with cut-off wavelengths from 200 nm (AIN) to 365 nm (GaN) can be fabricated from this alloy system. The direct bandgap of AlxGa1xe2x88x92x N-based detectors are also expected to have better intrinsic solar blindness than any other UV photodetectors. This makes them ideal for many applications, such as the surveillance and recognition of spacecraft, space-to-space communications, the monitoring of welding, as well as engines, combustion chambers, and astronomical physics.
Further, GaN, InN AlN and their alloys (III-Nitrides) have direct bandgap energies from 1.9 eV (659 nm) to 6.2 eV (200 nm, which cover almost the whole visible down to mid-ultraviolet wavelength range. Therefore, one of the most important applications of these materials is to make visible and ultraviolet light-emitting diodes (LED) and laser diodes (LD) with high quantum efficiency, which are immediately needed in the current commercial markets and can be best achieved by these materials.
The performance of photoconductors and simple p-n junction photodiodes can be very limited in terms of speed, responsivity and noise performance. The optimization of GaN-based UV photoconductors requires sophisticated structures such as p-i-n layered structures, heterostructures or even quantum wells.
To fabricate these structures and achieve high-performance photodetectors, two critical issues need to be addressed. One is the high resistance of the p-type layer and its contact, which introduce signal voltage drop and excess noise at the contact point. The other problem is introduced by the p-type layer annealing procedure. The best way to illustrate these two problems is to describe their effect on the performances of current blue laser diodes.
Currently, the demonstrated blue laser diodes are not significantly practical since they have to be operated either in pulsed mode or CW at low temperature. In addition, their lifetime is short. A typical reported blue laser diode structure is a p-n structure with a p-type layer on top. Because of the high resistance of the p-type layer and its contact, excess heating at high current densities is generated, which leads to the failure of the device. Other problems exist as a result of the growing procedure, which are as follows: First, n-type layers are grown, followed by InGaN MQW; Mg-doped layers are then grown. Finally, thermal annealing at about 700xc2x0 C. or low-energy electron beam irradiation (LEEBI) is performed to convert the top GaN:Mg to p-type. Both of these procedures will deteriorate the quality of the bottom layers, including the promotion of defect and impurity propagation, interface deterioration and, worse than that, the dissociation of the InGaN active layer and interface quality of the InGaN multi-quantum-well, since InGaN begins to dissociate at temperatures above 500xc2x0 C.
With regard to emitters, III-Nitride based LEDs have been recently successfully developed and commercialized, providing coverage from yellow to blue. Further, blue laser diodes are known in pulsed mode at room temperature and continuous mode at about 40xc2x0 C. Blue or short-wavelength laser diodes are in demand primarily because of their immediate need in optical storage and full color flat-panel display. The optical storage density is inversely proportional to the square of the wavelength of the read-write laser diode. By simply replacing the currently used laser diode (780 nm) with blue laser diode (410 nm), the storage density can be enhanced by almost four times.
An object, therefore, of the invention is a III-Nitride alloy for use in photoconductors and diodes having high quantum efficiency.
A further object of the subject invention is a GaN-based MQW composition in a p-i-n structure of high quality.
A still further object of the subject invention is an alloy of the composition GaN/GaxIn1xe2x88x92xN in a standard p-i-n structure.
Those and other objects are attained by the subject invention wherein a GaN/GaxIn1xe2x88x92xN alloy (X=0xe2x86x921) is grown by MOCVD procedure in a p-n structure (no aluminum need be present, if desired) with the n or p-type layer adjacent the substrate. In the method of the subject invention, buffer layers of n-type material are grown on a substrate. The active layers, and confinement layers of p-type material are next grown. The structure is masked and etched as required to expose a surface. An n-type surface contact is formed on this exposed surface, and a p-type surface contact is formed on the masked areas, to provide good quality device performance.